This invention relates to a process for preparing a tetrabromobisphenol-A predominant product which has a low organic and HBr impurity content.
4,4'-isopropylidenebis(2,6-dibromophenol) is a well known commercial flame retardant and is usually referred to a tetrabromobisphenol-A (hereinafter "TBBPA"). The literature is replete with processes for the manufacture of TBBPA, see, for example, U.S. Pat. Nos. 3,234,289, 3,363,007, 3,546,302, 3,868,423, 3,929,907, 4,013,728, 4,036,894 and U.S. Pat. No. 4,701,568. Two process which produce TBBPA predominant products having particularly low organic impurity contents are described in U.S. Pat. No. 4,628,124 and U.S. Pat. No. 4,783,556.
In the '124 process, a methanol-bromine solution is added to a methanol-bisphenol-A solution with vigorous agitation. In this process the methanol-bromine solution is conveniently added in a dip-tube beneath the surface of the methanol-bisphenol-A solution. The process in U.S. Pat. No. 4,783,556 is similar except that a product having a lower organic impurity content is obtained by impinging a methanol-bromine stream and a bisphenol-A and methanol containing stream in an impingement mixer and then conducting the resultant mixture to a reaction vessel. It has been found that this procedure, while yielding a very pure product as far as organic impurities is concerned, is not superior to the '124 process in regard to the HBr content of the TBBPA predominant product.